3. Calculation model
The geometry of the MCHE used in this study was designed by Ngo for use in a residential heat pump system [3]. The copper heat exchanger comprises cold water channels and hot CO2 channels. The top view and cross-sectional view are depicted in Fig. 4. The whole heat exchanger size is 1240 68 4.75 ( mm ).
The simulation calculations were examined separately for the hot and cold side to attain accurate empirical correlations using small temperature differences.
The cold (water) side includes large S-shaped fins in its flow channels. The calculation model of the cold side is presented in Fig. 5. The model size is 90.78 12.37 1.35 (mm), which is almost 0.42% of the whole heat exchanger volume. Regarding boundary conditions, the periodic condition was applied to both side walls. The bottom plane is the symmetrical plane. Furthermore, the top wall temperature was 2 C higher than the fluid inlet temperature all the way along the channel. The inlet temperatures were 278.15 K and 358.15 K, to simulate a part near the inlet and outlet of the heat exchanger. The flow rate was 6.04 1041.75 103 kg/s.